U.S. patent application Ser. No. 11/432,826, filed May 12, 2006 and entitled “COMBINED GASIFICATION AND VITRIFICATION SYSTEM” (hereafter the “combined system” and incorporated in its entirety herein by this reference) disclosed an improved method for processing organic and heterogeneous feedstocks. The description of the combined system describes a system that is capable of treating mixtures of inorganic materials, biomass, and fossil-based organic materials and their derivatives, including waste derived from the production and use of such fossil-based organic materials, and converting them into a clean fuel gas and an environmentally stable glass. The combined system consists generally of a gasification unit which converts all or a portion of the organic components of waste to a hydrogen rich gas and ash in communication with a joule heated vitrification unit which converts inorganic materials and ash formed in the gasification unit into glass, and may further include a plasma which converts carbon and products of incomplete gasification formed in the gasification unit into a hydrogen rich gas.
As described in the combined system, organic or heterogeneous mixtures of organic and inorganic feed stocks are first fed into the gasification unit where all or part of the organic portion of the feed stock are gasified. To assist in gasification, the materials are mixed with oxygen in the gasification unit using oxygen, air, carbon dioxide, oxygen enriched air, steam, and combinations thereof.
Within the partial oxidation gasification system, all or part of the organic portion of the feed stock is gasified. The effluent from the gasification process includes a gaseous portion, principally made up of carbon monoxide, hydrogen, and light hydrocarbon gasses, together with a solid and liquid portion, which includes unreacted and partially reacted organic materials such as carbon char, together with the inorganic portion of the feed stock, which may also include ash from the gasification process.
The effluent is then fed directly from the gasification system into a joule heated plasma reaction chamber to pyrolize and gasify the remaining solid and liquid organic materials, and to allow sufficient residence time and mixing to form the ash and other remaining inorganic portions of the feed stock into stable, vitrified glass.
The combined system further includes a feedback control device which measured effluent gasses, the flow rates of the feedstock, and the flow rates of the oxidant. Using that information, the feedback control device determines whether complete combustion was occurring in the gasification unit. Having recognized an undesirable operation, the feedback control device could then change the feed rates for one or both of the oxidant or the feedstock, thereby preventing complete combustion in the gasification unit.
For example, if the gasification unit is configured as a downdraft gassifier, the feedback control device could control a means for transporting organic material down the axial length of the downdraft gassifier. In this manner, the flow rate of the feedstock through the gassifier could be increased or decreased. The combined system disclosed several means for transporting organic material down the axial length of a downdraft gassifier and into the vitrification system including, but not be limited to, an auger, a rake, an agitating grate, one or more rotating drums, a piston, and combinations thereof.
While the agitating grate described in the combined system generally accomplishes the purposes of the combined system, the present invention overcomes drawbacks discovered when using an agitating grate as described in the combined system. Nevertheless, the present invention should not be limited to use in the combined system. Rather, the present invention is broadly applicable in any high temperature system where there is a desire to transfer solid materials at a controlled rate from one chamber to another. Accepting that caveat, and not meant to be limiting, it is useful for illustrative purposes to describe the advantages of the present invention in terms of some of the drawbacks of the agitating grate used in the combined system to enhance an understanding and appreciation of the present invention.
One difficulty that the combined system was designed to overcome was the failure of prior art systems to effectively and efficiently process heterogeneous feed stocks. One aspect of these heterogeneous feed stocks related to the agitating grate interposed between the gassifier and the joule heated melter of the combined system is the tendency of certain materials to block or plug different parts of the grate. When that happens, the gas flow circumvents the blocked or plugged section of the grate, and flows to the unblocked or unplugged sections. This, in turn, causes more rapid oxidation of the materials in the unplugged sections, and slower oxidation of the plugged sections, further exacerbating the problem as the more oxidized portions are reduced in size and thus generally flow through the grate while the less oxidized portions are not reduced, and tend to add to the clogged area of the grate.
Accordingly, there is a need for an improved means by which materials processed in one chamber of a high temperature system may be transferred to a second chamber of the high temperature system.